Alzheimer's disease is a neurodegenerative disease having pathological characteristics of degeneration and loss of nerve cells, senile plaque formation, and neurofibrillary tangle. Alzheimer's disease induces a cognitive impairment that a memory, recognition, thinking, judgment, and the like are lost progressively, and finally leads to death.
The main substance of the senile plaque deposited in the brain is amyloid β peptide (Aβ peptide) composed of 39 to 43 amino acids. Aβ peptide shows cytotoxicity, and this is considered to induce Alzheimer's disease (Non-Patent Document 1). Aβ peptide secreted from cells is a polypeptide mainly composed of 40 or 42 amino acids. It is known that, among other Aβ peptides, an Aβ peptide composed of 42 amino acids is aggregated strongly, is deposited in the brain early, and has strong cytotoxicity (Non-Patent Document 2). Accordingly, a medical agent for inhibiting production of Aβ peptide and a medical agent for inhibiting aggregation of Aβ peptide are expected to be useful as a preventive and/or therapeutic agent for Alzheimer's disease.
Concerning a medical agent that inhibits production of Aβ peptide, studies have been focused on a substance capable of inhibiting β-secretase and γ-secretase, which are enzymes involved in production of Aβ peptide. In addition, an Aβ peptide degrading enzyme promoter, an anti-Aβ peptide antibody, a medical agent that inhibits aggregation of Aβ peptide, or the like have also been studied.
On the other hand, there have been reported that a Met-oxidized Aβ peptide (i.e., an oxidized product of Aβ peptide in which the sulfur atom of the Met residue has been oxidized) is present in a low amount in the living body, and the Met-oxidized product has lower aggregation than Aβ peptide (Non-Patent Documents 3 to 5).